1. Field of the Invention
The present invention relates to a steering wheel of a vehicle such as a motor vehicle which is operated to be turned in changing a traveling direction or a reversing direction of the vehicle.
2. Description of the Related Art
As one mode of a steering wheel, there is a steering wheel which includes an air bag module for protecting the driver of a vehicle such as a motor vehicle from impact that would be exerted on the driver when the impact is applied to the vehicle from the front thereof (for example, refer to JP-A-2013-71626). As shown in FIG. 10, this steering wheel also includes a horn switch mechanism which activates a horn module 60 to operate in addition to an air bag module 50.
The horn switch mechanism includes an elastic member 51, a support member 52, a slider 53, a spring 54, a cap member 55 and a movable-side contact portion 56. The elastic member 51 has an annular shape and is mounted on a bag holder 57 of the air bag module 50. The support member 52 is supported in a metal core 59 of the steering wheel in such a state that the support member 52 is inserted through the elastic member 51. A rear end portion of the support member 52 constitutes a fixed-side contact portion 52a. The slider 53 is disposed so as to slide in a front-to-rear direction relative to the support member 52 between the elastic member 51 and the support member 52 and is biased to the rear by the spring 54. The cap member 55 contacts a rear end portion of the slider 53 and covers at least the end portions of the support member 52 and the slider 53 from the rear. The movable-side contact portion 56 is installed inside the cap member 55 and is connected electrically to the horn module 60 by way of the bag holder 57 and the like.
In the steering wheel having the horn switch mechanism which is configured in the way described above, the movable-side contact portion 56 is spaced away to the rear from the fixed-side contact portion 52a when the air bag module 50 is not depressed. This cuts off an electrical communication between the contact portions 52a, 56, and hence, the horn module 60 is not activated. In this situation, the air bag module 50 functions as the mass of a dynamic damper, and the elastic member 51 functions as a spring of the dynamic damper. Because of this, when the steering wheel vibrates, the elastic member 51 vibrates together with the air bag module 50 at a resonant frequency of the same as or near a frequency at which the steering wheel vibrates while being elastically deformed to thereby absorb vibration energy of the steering wheel. This absorption of the vibration energy restricts (dampens) the vibration of the steering wheel.
On the other hand, when the air bag module 50 is depressed, the force exerted on the air bag module 50 is transmitted to the movable-side contact portion 56 and the slider 53 via the cap member 55. Then, the slider 53 is pressed by the cap member 55 and is then caused to slide to the front against the spring 54. Additionally, when the movable-side contact portion 56 moves to the front together with the cap member 55 to be brought into contact with the fixed-side contact portion 52a of the support member 52 to thereby establish an electrical communication therebetween, the horn module 60 is activated to operate.
The steering wheel is constructed, as has been described above, so that the force applied to the air bag module 50 is transmitted directly to the slider 53 via the cap member 55. Because of this, when the air bag module 50 is depressed to activate the horn module 60, the slider 53 which is pressed by the cap member 55 is caused to slide to the front while compressing the spring 54. This increases the operation load of the air bag module 50 according to the operation or depression amount thereof when the air bag module 50 is depressed to thereby improve the operation feeling of the air bag module 50.
However, the steering wheel is constructed so that the rear end portion of the slider 53 rubs against the cap member 55 at all times while the weight of the air bag module 50 being exerted thereon. Thus, in attempting to restrict (dampen) the vibration of the steering wheel by the air bag module 50 (the damper mass) and the elastic member 51 (the spring), the resonant frequency is not stabilized depending upon how the rear end portion of the slider 53 rubs against the cap member 55. Additionally, the resonant frequency tends to fluctuate as the vibration which is inputted from the vehicle (the motor vehicle) side fluctuates. For example, when a small magnitude of vibration is inputted, the sliding resistance of the slider 53 against the camp member 55 becomes dominant in relation to the resonant frequency, resulting in a tendency for the resonant frequency to become high relatively.